Signaling system



J. W. HORTON SIGNALING SYSTEM Nov. 3, 1925.

Filed Jan. 6. 1923 mm, U

Any.

Patented Nov. 3, 1925.

UNITED STATES JOSEPH W. HORTON, 0F BLGOMFIELD, NEE-V COMPANY, INCOPt-PSRATED, OF

JERSEY, ASSIGNOR TO \VESTERN ELECTRIC hlE-vV YQRK, N. Y., A COR-PGBAZION OF NEN YORK.

SIGNALING SYSTEM.

Application filed January 8, 1923.

To all 1071 am it may concern Be it known that I, Josnrrr TV. HORTON, a citizen of the United States, residing at Bloomfield, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Signaling Sys tems, of which the following is a full, clear, concise, and exact description.

This invention relates to a carrier current ystenn and more particularly to a carrier current telephone system.

Among the objects of the invention is to produce such a system wherein the usual ringing, supervisory and other signals incident to the establishing of a connection between subscribers are eiticiently transmitted without impairing the speech transmission efficiency thereof.

A high frequency carrier current telephone channel is ordinarily coupled to a low frequency line over which low frequency si naling currents and audio frequency currents are transmitted.

The low frequency signaling currents are ordinarily translated into currents of higher frequency for modulating the carrier currents, and the modulated carrier currents are transmitted over the carrier channel.

In order that a carrier current telephone system may be most efficient, the apparatus thereof is designed for carrier currents modulated by audio frequency currents.

Therefore, to attain an object of this invention the modulating signaling currents are of audio frequency.

In accordance with a feature of this invention balanced modulators and demodulators are employed in the transmitting and receiving channels respectively of a carrier current telephone system and two signaling currents of different audio frequencies are employed to modulate the carrier current.

These modulating signaling currents are simultaneously impressed upon the modulator.

The transmitted carrier currents moduluated in accordance *ith such audio frequency signaling currents upon being re ceived are demodulated by the balanced demodulator.

A combination, such as the difference fre quency currents, of the audio frequency modulating currents produced by the demodulator is utilized to control the applierial No. 610,976.

cation of low frequency signaling current to the low frequency line.

Modulating signaling current of frequencies other than audio frequencies may, of course, be employed.

The invention will be described as applied to a multiplex carrier current telephone system employing guided carrier waves, although it will be understood that it is also applicable to such a system employing unguided carrier waves, as well as to a carrier current telegraph or other system.

The drawing illustrates diagrammatically only so much of a multiplex carrier current telephone system as is necessary for an understanding of the invention.

The apparatus and circuits illustrated are located at the junction between a line L over which low frequency oscillations are to be transmitted, and a line ML over which modulated high frequency oscillations are to be transmitted.

The low frequency line L, according to the customary practice, may extend to and terminate at a telephone switchboard.

The high frequency line ML extends to a distant junction (not shown) between such lineand another low frequency line similar to L, at which distance junction apparatus and circuits similar to those illustrated are providech The low frequency and high frequency lines L and ML are connected by an outgoing high frequency transmitting channel TL, an incoming high frequency receiving channel RL and a high frequency transmitting and receiving line TRL common to the several channels TL, BL and TL. RL of the multiplex c2 rier current system.

The high frequency transmitting and receiving channels TL and RL are associated with the low frequency line L through transformer 1.

The two channels TL and BL are rendered substantially conjugate by the PIOVlsion of an artificial line or net AL to balance the line L.

The line TRL, common to the several transmitting and receiving channels, 18 mductively coupled to the main line ML through a transformer 2. q

The main line ML may, of course, be utllized for the transmission of audio or lower frequency oscillations, high pass and low signed to the channel are supplied to the modulator M from a carrier current source CS. 1

Currents of modulating frequency are supplied to the modulator through the transformer 3.

The modul'ator 'is so organized that carrier currents are not transmitted thereby unless unbalanced when modulating oscillations are" impressed thereon;

The band filter TBF is of the general type disclosed in U.-S. patents to George A.

Campbell Nos, 1 1,227,113 and 1,227,114, dated May 22,191? It is designed to pass only currents of frequencies 'Within either the u er or lower side band and to sun ress I .L I,

currents of all other frequencies.

Tf'The incoming or receiving channel R-L includes a band filter RBF similar to the band filter TBF, a demodulator DM and a lovv pass'filter LPR'. 1

The demodulator DMpmay be of any Well-knowntypebi1t, as illustrated, is of the balanced type disclosed in U. Sflpatent to JohnR. Carson, No. 1,343,308, issued June Such a balanced 1 demodulator operates upon the homodyne method of receiving and 1s, therefore, supplied from the circuit 4 with "oscillations' ofthe carrier frequency cies.

' which functions in a manner Well underassigned to the-channel; i r

The oscillations suppliedfrom the circuit 4 react ina'Well-knon'n manner 'With the received modulated osci lations 'to detect the low frequency modulating currents.

The low pass filter, which may be of thetype disclosed in the Campbell patents hereinbefore referred to, permits'the passage of the currents of the modulating frequenc es but suppresses currents of higher frequen- The system thus far described is a carrier current telephone system of the usual type stood by those skilled in the art.

It iscustOma-ry to ring over low frequency tuned to such difference frequency currents telephone lines, such as L, currents of low frequency such as, for example, 16 cycle currents ordinarily being employed.

Such lOW' frequency currents are not as suitable for modulating the carrier currents as currents of'higher frequency.

Hence it is usual, as illustrated in U. S.

patent to Aifel and Davidson, No. 1,402,202, January 3, 1922, to provide at the junction between the low frequency line and the carrier system apparatus controlled by such low frequency currents which in turn controls the application of higher frequency modulating currents to the carrier system.

The lOW frequency line L is, therefore,

provided Witha ringing response relay 5,

Which through a relay12, controls the application of modulating oscillations to the modulator M. r

The modulating oscillations are two currents of different audio frequencies f, and f supplied over a line 6.

The source of the two currents of different audio frequencies may be common to the several channels of the'system. Aparticular advantage of the use of modulating currents of audio'frequencies for signaling purposes in a carrier telephone system is that no special intermediate apparatus need be provided in the high freeuency line or in the path of carrier cur 'rents modulajed in accordance with speech frequencies.

Another advantage is that closer frequency spacing of the several carrier channels may be employed whereby a greater number of channels may be provided Within a given frequency range. V

In order to provide for the necessary translation of ring'ng currents from main line ML to line L, a re ti ier R- is associated with the demodulator DM, to rectify a combination of the modulating currents. The rectified currentscause the operation of a relay 7 which controls the operation of relay 8 to apply sixteen c cle ringing current to line L.-

The input circuit of rectifier R is inductively coupled through a transformer 9 to the common branch of the output circuits of the demodulator DM,.

The common branch of the demodulator output circuits includes the transformer primary and a condenser 10, which cooperate to tune the common branch to a combinat on component of the modulating currents,

preferably, that of their difierence frequency. i 1

The common branch is in balanced relation to the circuit traversed by speechcun rents, so making it sharply resonant to the Cll'ffQlGDCE frequency Wave of the received -.line currents has no disturbing effect upon the transmission of the speech currents.

The input c'rcuit of the rectifier R 1s also through the provision of a condenser 11 to cooperate With the transformer secondary windings.

The operation of the ringing feature of the system will now be described.

Sixteen cycle ringing current incoming from the line L actuates ringing response relay 5 which opens the circuit of relay 12. Relay 12, in releasing its armatures, applies the two modulating currents of different audio frequencies f, and 7, from the circuit 6 to the input of the modulator M. The modulating currents so applied modulate the carrier current from the source CS, the balanced modulator operating to eliminate the unmodulated carrier component. The modulated carrier currents are then transmitted to the band filter 'IBF which suppresses one of the side bands. The other side band is transmitted over the common transmitting and receiving line TRL and through the transformer 2 to the main line ML.

Carrier currents modulated in accordance with the two currents of audio frequencies f and f incoming from the line ML are transmitted into the common circuit TRL and are selected by the filter RBF The modulated carrier currents transmitted through the filter RBF are impressed upon the input circuit of the balanced demodulator DM where they react with the unmodulated carrier current supplied from circuit 4, and also with each other. Currents resulting from the interaction of the received line currents with the unmodulated carrier current are of the frequencies f and f Such currents of these frequencies are balanced out in the common branch of the demodulator output circuit, but are impressed upon the low frequency output circuit RL The interaction between the two'components of the received line currents results in currents of frequencies f +f and f f which appear in the common branch but not in the low frequency output circuit RL since they are balanced out in the output transformer. Since this common branch is tuned to the difference frequency currents of the received line currents, the difference frequency currents are transmitted through the transformer 9 and are impressed upon the input circuit of the rectifier R. Relay 7 responds to the rectified currents and causes the operation of relays 8 and 13. Relay 8 disconnects ringing response relay 5 from the line L and connects thereto 16-cycle ringing current. Relay 13, in operating, short-circuits the primary windings of transformer 3, thus preventing interference during the application of 16-cycle ringing current to the line L.

The invention set forth herein is, of course, susceptible of various other embodiments and adaptations.

The invention claimed is:

1. In a signaling system, means for transmitting a carrier wave modulated by 0scillations of a plurality of different frequencies, a balanced demodulator having output circuits provided with a common branch, means for impressing said modulated wave upon said demodulator, means for impressing an unmodulated carrier wave upon said demodulator, whereby the demodulator produces in the common branch currents whose frequency is a combination of the modulating frequencies, and a signal controlled by the currents in said common branch.

2. In a signaling system, means for transmitting a carrier wave modulated by oscillations of two different frequencies, a receiving circuit therefor, a balanced demodulator associated with said receiving circuit and having a common branch tuned to a frequency comprising a combination of the modulating frequencies, and a signaling device associated with said tuned circuit.

3. In a signaling system the combination of a balanced demodulator having output circuits provided with a common branch, means for impressing upon the demodulator unmodulated carrier currents and carrier currents modulated in accordance with two different frequency currents whereby the demodulator produces in the common branch currents whose frequency is a combination of the modulating frequencies, a rectifier coupled to the common branch to rectify the combination currents, and a signal controller responsive to the rectified currents.

4-. In a signaling system, the combination of a balanced demodulator having output circuits provided with a common branch, means for impressing upon the demodulator unmodulated carrier currents and carrier currents modulated in accordance with two different frequency currents whereby currents whose frequency is the difference of the modulating frequencies are produced in the common branch, and a rectifier coupled to the common branch to rectify the difference frequency currents of the modulating currents.

5. In a. signaling system, the combination of a balanced demodulator having output circuits provided with a common branch, means for impressing upon the demodulator unmodulated carrier currents and carrier currents modulated in accordance with two different audio frequency currents whereby currents whose frequency is a combination of the modulating frequencies are produced in the common branch, means for tuning the common branch to the combination frequency currents, and a signal controller controlled by the combination frequency currents.

6. In a signaling system, the combination of a balanced demodulator having out put circuits provided with a common branch, means for impressing upon the demodulator unmodulated carrier currents and carrier currents modulated by two different frequency currents whereby currents whose frequency is a combination of themodulatin'g frequencies are produced in the common branch, and means to tune the common :branch to the combination frequency cur- 5 rents.

'10 rier currents and carrier currents modulated accordance with two currents of different frequencies whereby currents whose frequency is the dlfference of the modulating at frequencies are produced in the common branch, and means to tune the common branch to the dlfference frequency currents;

8, A signaling system comprising a low ffrequency line, a high frequency line, a car- WZO rier receiving channel betweenthe low and high frequency lines, a balanced demodulator in the receiving channel, means for impressing upon the demodulator unmodulated carrier currents and carrier currents incoming over the high frequency line and modulated in accordance w1th two currents of different audlo frequencies, whereby currents whose frequency is acombination of the. modulating frequencies are produced by vE the demodulator, and

the combination frequency currents to im-i press currents of another frequency upon the means controlled by low frequency line. 7

9. In a signaling system, the combination a source of high frequency carrier currents, a source of carrier currents modulated by two currents of different lower frequencies, means including a demodulator upon' which the unmodulated and modulated car-' 'rier currents are impressedto produce cur- Qre nts whose frequency is a combination of j the modulatlng'frequencies, meansto rectify the combination frequency currents, and a signaling element responsive to the rectified currents.

10. In combination, means for producing and tranmsitting a carrier wave simultaneously modified in accordance with a plurality of lower frequency waves, a receiving circuit therefor including a balanced demodulator having a common branch tuned to a frequency comprising a combination of said lower frequency waves, a calling device, and means controlled by the currents in said tuned branch to energize said calling device.

11. A telephone transmission system comprising means for producing and transmitting a carrier wave, apparatus for modulating said carrier wave in accordance with speech, a receiving stat-ion comprising means for receiving 'said carrier wave and demodu- "l ating it to reproduce the transmitted speech signal, means for impressing two different frequency waves well within the range of essential speech frequencies together upon said modulating apparatus during a nontalking period, and means connected to said demodulating apparatus responsive to a combination frequency wave of" said two different frequency waves to produce a signal indication.

12. The method of calling in carrier wave transmission which comprises simultane ously modulating the transmitted carrier wave with two different frequency waves lying well within the range of essential speech frequencies, deriving from said modulated wave at a receiving station a wave of a combination frequency of said two different frequency waves and utilizing said derived wave to'produce a ringing signal.

In witness whereof, I hereunto subscribe my name this 4th day of January A, 1).,

JOSEPHYV. HORTON. 

